Technical Field
Disclosed herein are fan blades for gas turbine engines and methods of manufacturing such fan blades. The disclosed fan blades include low thermal conductivity abrasive-coated tips for engaging an abradable liner that surrounds the fan blades.
Description of the Related Art
FIG. 1 illustrates part of a turbofan gas turbine engine 10. The engine 10 may include a nacelle 11, which may be lined with a fan case 12 that may include a liner 13 that surrounds the distal tips 14 of the fan blades 15. The fan blades 15 may each include a leading edge 16, a trailing edge 17 and a base or root 18, which may be coupled to a rotor 21. The rotor 21 may be coupled to a low-pressure shaft 22 via a fan shaft 23 and fan shaft extension 24. Also shown in FIG. 1 is a low-pressure compressor 25, an annular bypass duct 26 and part of the high-pressure compressor 27. Downstream components such as a combustor and high and low-pressure turbines are not shown.
The liner 13 may be coated with an abradable coating that is not shown in FIG. 1. Abradable coatings may be used in gas turbine engines in the fan section where a minimal clearance is needed between the blade tips 14 and the liner 13. Abradable coatings may also be used in the compressor and turbine sections. The abradable coating may be designed to wear when engaged by the more abrasive fan blade tips 14, thereby reducing or limiting wear to the fan blade tips 14. By using abradable coatings on the liners 13, closer clearances between the blade tips 14 and the liner 13 may be employed, which results in improved efficiency. Further, as the abradable coatings wear, the coatings can act to automatically adjust the clearance between the liner 13 and blade tips 14, in-situ. Typical abradable coatings include epoxy with a filler, such as glass microballoons, which reduce density and weight and also provide a low thermal conductivity coating.
Aluminum fan blades 15 for gas turbine engines 10 may be coated with an erosion resistant coating, such as polyurethane, to protect the aluminum. Such erosion resistant coatings have also been applied to composite fan blades as well. One problem associated with polyurethane coatings is their tendency to degrade if the fan blade gets too hot. More specifically, as a hard-anodized fan blade tip 14 rubs against the abradable coating of the liner 13, frictional heating causes the blade tip 14 to get hot enough to degrade the polyurethane coating of the fan blade 14.
Accordingly, there is a need for improved fan blades that do not get hot enough to damage erosion resistant coatings during use.